1. Field of the Invention
The present invention is concerned with a direct current voltage regulating circuitry which is connected in series between an unregulated DC supply source and a load to which a current is supplied from said DC supply source to keep the applied voltage constant. More particularly, the present invention pertains to a series DC voltage regulating circuitry of the continuously controllable type which is arranged such that a variable resistance element is connected in series in the load current path, to be operative so that in case the voltage applied to the load, i.e. the output voltage, varies from its set value resulting in a deviation, the internal resistance of the variable resistance element is increased or decreased in accordance with the variation of the output voltage, whereby this output voltage is kept at the set value.
2. Brief Description of the Prior Art
A series DC voltage regulating circuitry of the continuously controllable type is comprised, basically, of: a variable resistance element connected in series to the load current path; an output voltage detecting circuit for providing a voltage proportional to the output voltage; a reference voltage source for generating a reference voltage; and an error amplifier for comparing the voltage proportional to the output voltage detected with the reference voltage by means of a detecting circuit and to amplify the resulting error (difference between the two) voltage and to supply this amplified error voltage to the control terminal of the variable resistance element (There may be an instance where said comparison and said amplification of the error voltage are performed by respectively separate circuits.).
Of the aforesaid component elements of the regulating circuitry, the error amplifier and the reference voltage source constitute the most important parts of the circuitry, and accordingly the ability of the whole circuitry is substantially determined by the abilities of these constituting elements. The reference voltage source must be one which always generates a certain constant reference voltage. For example, when the reference voltage is changed due to the change in the ambient temperature, this voltage change will in turn result in a drift of the output voltage. The error amplifier must also be such that its gain and the like are not affected by the fluctuations of the ambient temperature, and that it has a good linearity and a high gain.
In the past, a bipolar transistor has been used as the active element of the aforesaid error amplifier, whereas a voltage regulator diode such as a Zener diode has been used as the reference voltage source. However, the characteristics of such bipolar transistor and Zener diode are significantly affected by ambient temperature as is well known. For this reason, in the conventional DC voltage regulating circuitry, there have been attempts to additionally provide a temperature compensating circuit on both the error amplifier and the reference voltage source for compensating for the effects of the ambient temperature, or a need has been noted to use, in the reference voltage source, an expensive voltage regulator diode of a temperature-compensating type. Thus, the whole circuitry has tended to become complicated. Moreover, even in case such a temperature compensating element as stated above is provided, it has not been necessarily possible to obtain a sufficiently desirable result. Furthermore, there has been the problem that the necessitated increase of the required number of active elements and like parts has constituted an important cause of the degradation of reliability of the circuitry.
On the other hand, the DC voltage regulating circuitry is required so that its output voltage can be varied extensibly depending on its use. In the conventional circuitry having the aforesaid arrangement, however, the reference voltage is determined by the voltage regulator diode. Also, even in the event that the reference voltage is divided by, for example, a divider circuit to provide other reference voltages equivalently, there still is an increased fear that the stability of the reference voltage against, for example, ambient temperature becomes degraded. In addition, there has been a tendency to develop fluctuations of the gain and the linearity of the error amplifier and to develop a deterioration of the temperature compensating effect. Thus, it has been quite difficult to make it possible to change the setting of the output voltage as desired.